This application claims the priority of German application 196 47 130.3, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a damper valve arrangement, which is suitable for a hydraulic power steering system, the servomotor of which is designed as a hydrostatic motor unit or as a hydraulic displacer unit and also acts as a steering damper, due the fact that at least one damper valve arrangement is provided in hydraulic lines between servomotor and servovalve, having at least one flow path which is controlled or throttled by damper valve elements.
Modern motor vehicles are regularly equipped with power steering, which at least in the case of passenger cars generally operates using auxiliary hydraulic power, in such a manner that the forces which the driver has to apply when steering the vehicle are always sufficiently low.
In order as far as possible to avoid or suppress fluctuations in the steering system, virtually all vehicle steering systems have a steering damper.
In this connection, it is known from German patent document DE-A 40 29 156 to enable a double-acting piston-cylinder unit, which serves as the servomotor, also to act as the steering damper, by providing damper valve arrangements in the lines between the piston-cylinder unit and the servovalve which is used to control the latter and via which the piston-cylinder unit can be connected in a controllable manner to a hydraulic pressure source and a relatively unpressurized hydraulic reservoir.
A fundamentally similar arrangement is described in German patent document DE-A 41 06 310.
It is known from German patent document DE-A 29 27 039 (=Great Britain patent document GB 2051714 A) to arrange in each case one non-return valve, which opens in the direction towards the respective piston working chamber and is provided with a throttle through-bore, at the cylinder-side connections of the lines which connect the servovalve to the double-acting piston-cylinder unit of a power steering system, the valve housing of which non-return valve may be formed by a screw which serves to fasten the respective line to the cylinder.
In order to simplify the damper valve arrangement, German patent document DE 43 23 179 A1 envisages providing the damper valves on a valve support part in the form of a perforated disc, the holes of which, through which the hydraulic medium passes, can be controlled by means of small valve plates held on the end side of the valve support part by bolts and/or by means of spring-mounted valve plates. There may be provision here for clamping the valve support part in the form of a perforated disc, in the manner of a spacer ring or a spacer disc, between a bearing surface of a connection stub arranged on the housing of the servo valve or of the servomotor and a mating bearing surface of the connection part, which can be connected to the connection stub, of the hydraulic line.
Instead of this, it is also possible to hold the valve support part captively in the connection stub or in the connection part, as is illustrated, for example, in German patent document DE 44 23 658 A1.
The power steering systems described above are extremely advantageous, owing to the dual function of the servomotor, which firstly generates a servoforce and secondly serves as a steering damper. Nevertheless, such designs remain extremely expensive, because the servomotor, which can be driven in two directions, must be provided on both sides with identically acting damper valve arrangements, in order to achieve an identical damping action in both directions of movement. Accordingly, it is always necessary for damper valve arrangements which are matched to one another in pairs to be present. However, since there are inevitable tolerances which result from the production of the damper valve arrangements, it is always necessary to hunt out pairs of damper valve arrangements with identical damping actions.
An object of the invention is to provide damper valves with extremely precisely defined characteristics.
This and other objects have been achieved according to the present invention by providing a damper valve arrangement, which is suitable for a hydraulic power steering system having a servomotor which is designed as a hydrostatic motor or displacer unit and also acts as a steering damper, said damper valve arrangement being provided in a hydraulic line between the servomotor and a servovalve, said damper valve arrangement comprising at least one flow path which is controlled or throttled by damper valve elements, and a bypass duct with a calibratable throttling resistance arranged parallel to the flow path.
The damper valve arrangement of the present invention utilizes a bypass duct with a calibratable throttling resistance parallel to the flow path.
The invention is based on the general idea of compensating for production tolerances in the damper valve arrangement by providing the ability to calibrate the throttling resistance. The fact that, according to the invention, the bypass duct with calibratable throttling resistance now provides a throttling path which can still be adjusted even after production of the damper valve arrangement means that the desired throttling effect of the damper valve arrangement can be defined extremely accurately, so that virtually any damper valve arrangements can be combined to form pairs with virtually identical parameters.
The invention takes into account the fact that the throttling resistance of a flow path changes to the extent of about the 5th power of the diameter of the flow path, and consequently even slight production tolerances lead to very different flow resistances. The possibility of calibrating the throttling resistance of the bypass duct allows this unavoidable effect to be compensated for.
According to a preferred embodiment of the invention, the damper valve arrangement has a support part in the form of a perforated disc and having a central axial peg, which, on the one hand, serves to hold spring-loaded valve plates and/or small valve-spring plates for controlling the flow paths formed by the holes in the perforated disc and, on the other hand, has an axial duct, which forms the bypass duct, passing through it, at one end of which duct is arranged a throttle element which leaves open a calibratable gap.
In a particularly preferred manner, it is provided for the support part to be arranged coaxially with respect to the screw axis and captively in a connection part, which has a cup-shaped interior, for holding a hydraulic line and divides up the interior between the open end and the closed end of the connection part, an axially adjustable pin, which is arranged coaxially with the bypass duct, being arranged as a throttling element at the closed end of the connection part, so that the throttling action can easily be calibrated.
As an alternative, it is also possible and advantageous to replace the abovementioned axially adjustable pin with a mandrel-like extension arranged fixedly on the connection part and to arrange the pin containing the bypass duct in an axially adjustable manner on the support part.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.